Not taking any stance on the matter of who's the hacker and what are their intentions, but Erdogan has compared the German and Dutch administration Nazi multiple times by now in public speeches, so the tweets content are pretty much his stance boiled down to 140 chars.
He is pushing for a referendum that remind Europe of how Nazi Germany started.
To "defame" someone it must be false or attack his honour. This hack is just going along the lines he traced.